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Powertran Cortex

74LS2001 replacement.

74LS2001 replacement.

Hi All,
Would anybody be interested in a plug in 74LS2001 replacement.
I've done a PCB (14mm x 28mm) for one based on the 1985 ETI article but using surface mount 74LS04 and 74LS74 IC's.
But the cheapest i can get the PCB made is £96 for any quanity up to 40 off.
Anybody interested in a assembled module for say £15 +P&P (or less if if more than 10 people are interested but i doubt that !) to help spread the cost.

Thanks,

Jim
 
I've been working on a new layout for the parallel card from the same 1985 article, which will provide utility for the E-Bus as well if I can get some of the bare boards made up.
 
Today is the day.

Today is the day.

In a couple of hours (lunchtime) i should be put in the final few chips (Ram) and powering the first newly built Cortex for quite some time.
I already had it powered yesterday, firstly without any IC's fitted to check current drain and then with all the basic chips fitted except for the ram.
There was some activity on the busses but i didn't expect much without the Ram fitted.
If that works i have all the chips to fully populate the board except the 74LS2001 replacement.
Still trying to get the pcb for that made, i had sneaked it onto a spare part of a PCB panel for a new product here at work but it's not gone into production yet :-(

Jim
 
It lives !!
Well, as far as displaying the Basic prompt on an old TV
I did try to take a picture of the TV but the camera wasn't very happy with that idea.
Couldn't do much else as i've not finished the keyboard yet.
Heres the board on my desk, excuse the mess !

cortex powered.jpg

Jim
 
Excellent! I just got some keyswitches in today, so I should be able to assemble a keyboard soon--of course, the key caps weren't with the switches, so I hay have to do some creative surgery on some of the other keyboards I have to get what I need. . .on the 74LS2001 replacement board, I can do a quick add of it to the ExpressPCB file for the Parallel board--then you have both the access to the E-Bus and a card to use on it too. . .assuming I got all of the details right on the board.
 
I know of one other individual trying to assemble a pair of cortices, so yours, mine, and theirs will add at least 5 to the known survivor list, Jim. Before we know it, we'll know where more than 20 cortices reside, though yours is only the second in a Cortex II case! :)
 
Hi Ksarul,
I should still be able to get the 74LS2001 board done as part of our productioon boards for work and if it fits into a spare space on the panel it won't cost me anything.
Luckily a current project has a set of funny shaped boards so there is a gap.
But it may be a few weeks or a month before these boards get made.
Unfortunatly we use avery obscure pcb package called Boardmaker which has no export options at all apart from Gerbers.
I can send you a copy of the gerbers for my board if you wanted to add it to your parallel board.
I've attached a screen shot of the board, i still need to double check it against the schematic, especially with the mistake in ETI.

To be honest i may well not use the Cortex 2 case, i much prefered the original case with the built in space for the floppy drives.
I'm actually probably going to fit it into a old XT PC case and use the PC power supply as well.
The keyboard can either be in a modified pc keyboard case or i'll use a PC keyboard with a PIC based interface doing PS2 to parallel keyboard interface conversion.

Jim

74LS2001.jpg
 
Just noticed the picture hasn't got the ground plane turned on, it just covers the complete lower layer of the PCB apart from the one short track.
A header will be soldered onto the bottom of the board with the legs then cut off flush on the top side, then the SM ic's will be soldered on the top side.
I wanted to keep it as small as possible.

Jim
 
Some issues with the new Cortex, apart from lack of lunchtimes to work on it.

First problem was no keyboard input, this turned out to be the keyboard encoder chip, it just wasn't oscillating, a new chip fixed that.
Second problem, the display is a very washed out dark grey text on a white background, i suspect it's not right, what colours should it be ?
Third problem, i can only enter text for a few seconds and then it either locks up or starts flashing random junk on the screen, reseting the board does nothing, i just get a blank screen.
I have to let it "rest" for 10 mins and then it will work again for a few seconds, obviously something is not happy.
I'm going to make up the status LEDS next so i can see what they do, then get busy with the scope/logic analyser.

Thanks,

Jim
 
Update.

Update.

With the new keyboard decoder the display resonded to keypresses but they were graphics characters as if you had graphics key pressed.
This turned out to be a duff 74LS251 chip, IC63 i swapped it with IC62 (same chip but used to read floppy jumpers etc) and the keyboard worked correctly.

The locking up after a few seconds seems to be the processor itself, if i keep it cold with freezer spray it will stay working.
I kept if frozen long enough to type in the colour bar test program and this confirmed that there is no colour output, so something else to find.

Anybody got a TMS9995 processor for sale at a sensible price ?

Given that all these chips were new and have been unused for almost 30 years i'm quite suprised how many have failed.

Thanks,

Jim
 
Jim Hearne said:
Given that all these chips were new and have been unused for almost 30 years i'm quite suprised how many have failed.

Thanks,

Jim
Click to expand...

Electronics tend to deterioriate extremely rapidly when not used. Especially capacitors.
So if you get anything that hasn't been used for 30 years, all sorts of problems can arise.
 
I'm used to it with caps, hence i fitted all new caps and resistors.
Chips i've not come across it as being such a problem before, maybe because these were never used until now, and it's different from 30 year old chips that are fitted in equipment and were used early in there life.

Thanks to somebody on this list i think i've a TMS9995NL-12 on it's way to me.

Jim
 
I've been pretty harried this week (the mother-in-law arrived for an extended visit yesterday), but I should be able to pop one into the mail on Monday, Jim.
 
Jim Hearne said:
Hi All,
Would anybody be interested in a plug in 74LS2001 replacement.
I've done a PCB (14mm x 28mm) for one based on the 1985 ETI article but using surface mount 74LS04 and 74LS74 IC's.
But the cheapest i can get the PCB made is £96 for any quanity up to 40 off.
Anybody interested in a assembled module for say £15 +P&P (or less if if more than 10 people are interested but i doubt that !) to help spread the cost.

Thanks,

Jim
Click to expand...

I'm new to the forum and am attempting to build 2 Cortex(s) from scratch. As you can imagine, I'm struggling to locate 2 SN74LS2001(s). Count me in.
 
coryklatt said:
I'm new to the forum and am attempting to build 2 Cortex(s) from scratch. As you can imagine, I'm struggling to locate 2 SN74LS2001(s). Count me in.
Click to expand...
Hi,
I'm still hoping to do the 74LS2001 pcb but by fitting it on some spare space on a PCB here for work.
Typically the boards i added it to aren't being ordered just yet but should be early next year.

I have found various errors and ommisions in the documention available, i'll upload my updated parts list later.
The Cortex 2 build manual is the most correct i've found if you are using the PCB's that were on Ebay recently.

Good luck,

Jim
 
Any progress on the build, Jim? Did the chips I sent you work out?
 
Unfortunatly, due the death of my girlfriends ex-husband we now have her son in the house and a lot of the contents of his house as well.
That in conjunction with moving into a smaller unit at work has meant i've had nowhere to setup the Cortex and the test gear.
However, next week there are 2 off 17' x 10' buildings being assembled in the garden, one for my metalwork workshop, and the other for a hobby room which my share of will be for my electronics stuff.
So, once i've insulated and lined them i should have plently of space to work on the Cortex.

Updates will be here as soon as i have something to update.

Jim
 
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